The competition between transitions 3s2-3p4 and 3s2-3p2 in a He-Ne laser is analysed quantitatively by rate equation, for two cases of the absorption cell filled with pure methane and with mixture of methane and air respetively. The condition for satisfying the two wavelength oscillation is obtained. The calculated results of the relative output power and the region of the two wavelength oscillation are in rather good agreement with experiments. A new structure is designed which increases the efficiency by more than 70%.